I love the intent and execution behind this. The implication of imprecision in the underlying data through rough looking "hand drawn" charts and graphs is a really smart design hack.
The same approach could be used for mockup apps/websites
Do a high-fidelity, fully realized html mockup, and you're more likely to get feedback about the little details like fonts, colors, icons, spacing, wording and maybe minor tweaks to the layout.
Draw a really low-fidelity mockup with a sharpie or on a whiteboard, and you're more likely to have a good discussion about fundamental layout/concepts, overall approach, etc, without anyone getting hung up bike-shedding about the details.
I think a lot of this has to do with perceived effort: if people think you spent hours building it, they're less likely to suggest a change that would throw most/all of your work out. This doesn't mean you can't or shouldn't prepare ideas/drafts beforehand if you want to, nor that you shouldn't increase the fidelity as you iterate.
I've tried many tools for this, but personally all the best and most fulfilling [early] design discussions I've ever had involved standing around a whiteboard.
There's AvaloniaUI, though, if you're looking for XAML, UI, and cross-platform.
It was inspired by the 'xkcd' matplotlib theme, which itself is delightful:
There's an excellent blog post by the author with many more illustrations but I can't find it right now. Edit: found it!
I write texts that are free, so I am unable to pay someone to do it. At this point I use Asymptote, which does a very good job in the accuracy area and is perfectly professional in appearance. But I just love these figures and I wish I could convince my computer to turn them out.
As for computer generating that style, I might look for brushes for Photoshop/GIMP/Illustrator/Inkscape that produce the style you are looking for, and then reverse engineer those or use scripting capabilities of whichever tool to produce the figures.
But sometimes photos or exported illustrations don't work e.g. when someone else (remote) needs an editable copy.
You can then add points/etc like a regular map, it'll load quickly and work on devices how users are used to.
Balsamiq has a good description of this philosophy on their "What are Wireframes?" page. Here are the summary points:
1. It makes it clear that this is not the final design.
2. It conveys that "this is all up for discussion".
3. It makes it clear that no code has been written yet.
In other words, don't trust these drawings! They are not finished product, or any kind of product.
There's a longer explanation of each of these points on the page (scroll down to "Why Do These Wireframes Look the Way They Do?"). Recommended reading for anyone considering this sketchy style of drawing: